Justin BieberSucking FaceWith His Opening Act

9/21/2010 5:00 PM PDT BY TMZ STAFF

Justin Bieber was locked in a serious make-out session with the chick who stars in his "Baby" music video ... but the shocking part -- it all went down in the back of a Honda!!! And TMZ has the photos.

The chick playing tonsil hockey with The Biebs is 16-year-old Jasmine Villegas -- who also happens to be the opening act on Bieber's concert tour.

The photos were taken on Thursday, September 9 in Venice, CA by some Canadian tourist who just happened to notice his country's most famous pop star in the midst of a make-out session with the luckiest teenage girl on the planet.

The two had been rumored to be dating ... but they insisted they were just "really cool friends."